Seismic surveying is used for identifying subterranean elements, such as hydrocarbon reservoirs, fresh water aquifers, gas injection reservoirs, and so forth. In performing seismic surveying, seismic sources and seismic sensors can be placed at various locations on an earth surface (e.g., a land surface or a sea floor), or even in a wellbore, with the seismic sources activated to generate seismic waves. Examples of seismic sources include explosives, air guns, acoustic vibrators, or other sources that generate seismic waves.
Some of the seismic waves generated by a seismic source travel into a subterranean structure, with a portion of the seismic waves reflected back to the surface (earth surface, sea floor, or wellbore surface) for receipt by seismic sensors (e.g., geophones, hydrophones, etc.). These seismic sensors produce signals that represent detected seismic waves. Signals from the seismic sensors are processed to yield information about the content and characteristics of the subterranean structure.
Often, time-lapse (four-dimensional or 4D) seismic surveying is performed, where the 4D seismic surveying involves acquiring multiple repeated surveys at different times. By using two or more seismic surveys acquired in time-lapse seismic surveying at different times, production-related or other development effects on a subterranean structure can be measured (e.g., effects as a result of production of hydrocarbons from a hydrocarbon reservoir). Each of the surveys conducted in the time-lapse seismic surveying will usually be irregularly sampled (acquired with irregular spatial sampling), and most likely, differently sampled.
As a result of the irregular and different sampling between surveys of the time-lapse seismic surveying, seismic processing algorithms employed on the repeated surveys of the time-lapse seismic surveying may produce differing results. Also, the image of the reservoir will differ for different surveys of the time-lapse surveying. The above effects may cause spurious differences between time-lapse surveys that may obscure the desired differences that are the objective of repeated measurements in 4D seismic surveying.
A further issue that affects time-lapse seismic surveying accuracy is overburden heterogeneity. “Overburden” refers to the geological area that overlies a target structure of interest (e.g., hydrocarbon reservoir) in the subsurface. Overburden heterogeneity refers to the fact that the overburden exhibits properties (e.g., velocity and density) that do not vary smoothly in the spatial and/or temporal sense. Instead, the overburden properties may vary rapidly, such as due to presence of rock fractures or harder and softer regions in the overburden.
A conventional solution for addressing overburden heterogeneity is to repeat source and receiver locations of each survey as accurately as possible to ensure that the pattern of seismic data distortion caused by the heterogeneity is the same in each survey. This can be accomplished by acquiring excess seismic data to increase the likelihood of well repeated trace pairs. This excess coverage provides an opportunity to select for subsequent processing, by 4D binning, the best repeated traces from a pair of time-lapse surveys.
Trace selection performed during 4D binning can adversely affect the quality of subsequent regularization performed to compensate for irregular data distribution in each seismic survey. Note that 4D binning and regularization are typically two independent operations performed separately, with regularization typically performed after 4D binning.